9 replies to this topic

[Choda Boy]

Just spent the weekend fitting my '91 998cc car with a Minisport stage one kit (including a single box exaust which sounds evil! ).
I havnt connected the water hoses to the inlet manifold yet though as im a bit confused on how exactly to do it.
In need of some advice and/or pointers!

Cheers

[Bungle]

it fits in the hose to the heater after the heater valve

[Big_Adam]

Just warms the manifold up for winter starts. Many leave it off, I recommend hooking it up tho.

[Choda Boy]

Yeh its just the heater valve on the hose i was wondering about. So if the hose goes through the inlet manifold before it comes to the valve, do you still get the hot water circulating through? I Do apologise if im just bein daft!

[Ethel]

Hot water leaves the heater valve and returns to the engine via the bottom hose.

Water in the manifold will warm the inlet and also cool it when the engine's hot.

I'd go for heater tap - heater matrix - manifold - bottom hose.

[vasi]

The purpose is to assist prevention of carb icing caused by the natural negative air pressure in the intake coupled with low Intake Air Temperature. It will not assist cold starts. If you have a cone filter fitted, you might connect it up as cone filters are a misguided performance enhancement.

[miniboo]

on a 1991 car though it may not have the heater tap on the head and actually have an inline one.

[Ethel]

I thought they still used the take of point but used a hose round the front of the head. but I didn't pick up on the point that Choda's car will have the remote plastic valve - shouldn't matter where the valve is it will still restrict the water flow whether it happens to be engine hot or cooler.

There's also nothing at all wrong with K&N type cone filters. If carb icing was a serious issue you'd do far better to heat the carb or at least the air BEFORE it enters it. I've run with performance filters for years, often in cold conditions, as I'm a winter sports enthusiast, and never had any cold running problems. I do know about the poor running and fuel economy caused by blocked filters which would surely cause an even greater pressure drop or "natural negative air pressure".

[Dan]

People call the cold manifold effect carb icing, but Ethel is right in that it isn't quite the same thing. An alloy manifold will run very cold if unheated, the original cast iron one is heated by the exhaust manifold as they are the same lump of iron. The problem with a very cold manifold surface is that it causes the fuel to condese out of the charge and form droplets on the surface which will then run into the cylinders as a liquid. Liquid fuel doesn't burn too well, petrol only burns as a vapour. This is why the carb is there, to atomise the fuel and the liquid petrol dripping into the cylinders does odd things. It makes the engine run poorly since it can't burn until it's evaporated meaning it burns later than the atomised fuel in the charge and you get a very unreliable burn as a result. Having warm manifold walls prevents this and doesn't really heat the charge very much. It does mean that the charge is almost always at the same temperature when it enters the engine and so the engine will stay in tune better nomatter what the whether was like when it was setup. This is what manifold heating is for and is why almost all road cars have heated manifolds. To keep it evenly heated all the time it is best to put it in parallel with the heater circuit so the valve won't turn it on or off. You need some heater hose and some coolant line tee pieces, it's easy enough. If you have the valve on the head you would need to convert to an inline valve to be able to run it like this but a 1991 car should have the inline valve already. Take coolant from the heater line before the valve, run it through the manifold and return it to the heater hose just before it meets the bottom hose.

Carb icing is different and is actually the formation of water ice crystals inside the carb due to low ambient temperatures coupled with the refridgerating effect of evaporating fuel and high humidity in the incoming air. It freezes the throttle spindle, jet and piston (in an SU) solid and really affects the running of the engine. SU carbs fitted to aero-engines (as used with Merlin and Griffin engines in the Spitfire and other fighters) had oil fed butterflies and throttle spindles and other engine heated parts to get around this. Minis and other BL cars sold to the Scandinavian market in the 70s had electrically heated carb suction chambers and carb bodies along with inlet manifold heating to combat both effects.

Edited by Dan, 11 July 2007 - 11:54 AM.

[Choda Boy]

Sounds helpful cheers dan. Does anyone have any pics or even some sort of simple diagram to help me visualise all this stuff before i commmit myself?!